1. Field of the Invention
The present invention relates to a polishing composition. More specifically, the present invention relates to a polishing composition to be used in a polishing step for forming e.g. a semiconductor device.
2. Discussion of Background
In recent years, along with the progress in the integration and speed of ULSI, etc. to be used for computers, a design rule of semiconductor devices has been progressively refined. To cope with an increase in electrical resistance of wiring due to such refinement of a wiring structure of a semiconductor device, it is considered to use a metal material containing copper, as a wiring material.
When a metal material containing copper is used as a wiring material, formation of a wiring structure by anisotropic etching is difficult due to the nature of the metal material. Therefore, it is common that such a wiring structure is formed by e.g. a method using chemical mechanical polishing (hereinafter referred to as a CMP method). Specifically, the following method is used. First, a barrier film made of tantalum or a tantalum-containing compound such as tantalum nitride, or a titanium compound or a ruthenium compound, is formed on an insulation film having wiring trenches engraved on its surface. Then, a conductor film made of a metal material containing copper, is formed on the barrier film so as to, at least, completely fill the wiring trenches. Then, in the first polishing step, a part of the conductor film is polished. Further, in the second polishing step, the conductor film is polished until the barrier film is exposed at portions other than the wiring trenches. Furthermore, in the third polishing step, the barrier film is polished until the insulation film is exposed at portions other than the wiring trenches, thereby to form wiring portions in the wiring trenches.
Heretofore, as a polishing composition, one comprising an abrasive such as silicon dioxide and various additives, has been considered. However, in a polishing method as described above, a conventional polishing composition was likely to polish a conductor film excessively, since it had a high stock removal rate against a metal material containing copper. In such a case, there was sometimes a problem of dishing observed on the polished surface after the polishing, i.e. a phenomenon such that the surface of the conductor film at portions corresponding to the wiring trenches, is recessed lower than the surface of the barrier film.
A polishing composition to suppress such dishing, has been considered. For example, Patent Document 1 discloses a slurry for CMP, which comprises a solvent, abrasive particles, at least one type of the first surfactant and at least one type of the second surfactant. In such a slurry, the first surfactant is one to improve the dispersibility of the abrasive particles and to increase denseness of a surface protective film to be formed on the surface of a metal film as a film to be polished during polishing, and the second surfactant is one to improve the dispersibility of the abrasive particles and to increase denseness and hydrophilicity of the surface protective film, and further to improve the hydrophilicity of the surface of a polishing pad to be used during polishing. However, as long as the present inventors know, if the denseness of the surface protective film becomes too high, an adequate stock removal rate could not sometimes be obtained although dishing may be suppressed, and thus, there was still a room for improvement. Further, in such a technique, the structures of surfactants themselves are significantly important elements, and it has been found that a suitable performance cannot be obtained simply by adding the two types of surfactants. For example, if a nonion surfactant having a large molecular weight, is used, a phenomenon is observed wherein the dispersion stability is deteriorated, and in the case of a surfactant having a high HLB, a phenomenon is observed wherein dishing becomes large.
Further, Patent Document 2 discloses a method of polishing a substrate having a metal layer containing copper by contacting it with a CMP composition comprising (a) abrasive particles, (b) an amphipathic nonionic surfactant having an HLB value of more than 6, (c) a means to oxidize the metal layer, (d) an organic acid, (e) a corrosion inhibitor and (f) a liquid carrier. However, as long as the present inventors know, even in such a method, it has been found difficult to reduce dishing while maintaining the stock removal rate, only by using the nonionic surfactant alone. Further, with a nonionic surfactant having an HLB of more than 12, it was difficult to reduce dishing.
Patent Document 1: JP-A-2002-155268
Patent Document 2: JP-A-2006-502579